To all:
Some thoughts on triggers.

If a single simple triggers pivot pin is located about 5/16-3/8 inch ahead of the sear arm the trigger will have a nice crisp 2-3 pound pull.

Due to the nature of a double set trigger the pivot pin for the front trigger is usually much further in front of the sear arm resulting in a heavy trigger pull if the rear set trigger is not 'set'.
There is no simple adjustment that can be made to correct this condition without buying a double set trigger which has a better design with the pivot pin located further aft, closer to the sear arm.

The little screw between the triggers on a double set trigger does NOT change the weight of the front trigger pull. It only changes the amount of engagement between the front trigger and the catch on the rear trigger.
Put another way, if this screw is screwed out the front triggers catch engages the rear triggers latch further resulting in a slightly greater amount of front trigger movement to release the rear trigger.
If the screw is screwed in to far, the front triggers catch may not catch the rear triggers latch making it impossible to 'set' the rear trigger.

Muzzleloading triggers designs follow the historical designs of the triggers made in the 18th and 19th century. They are not intended to be like a fully adjustable modern trigger where everything from release pressure to overtravel is adjustable. Folks wanting that sort of thing should consider shooting modern arms.

Triggers on many reproduction guns often have heavy pulls because the sear spring in the lock is much too strong.
This spring needs only to be strong enough to insure that the sear will fully engage the half-cock and full cock notches in the tumbler under all conditions. Lightening the force this spring produces will often reduce a very heavy trigger pull to a much lighter pull while still assuring the sears engagement with the tumbler.

Double set triggers which won't release the lock by simply pulling the front trigger while the rear trigger is left unset are very likely Double Set Single Lever triggers designed for target shooting.
They are also used to provide a 'set trigger' which will work with a flyless lock because often the rear trigger will be held forward by the heavy trigger spring keeping the rear triggers blade pushed up so that it holds the sear in a released condition.
The rear trigger must be set on triggers like this before a person can even cock the gun to a full cock position.
The front trigger on this type of double set trigger is designed only to release the rear 'set' trigger. It does not have the blade needed to trip the sear on the front trigger. The only fix is to learn to live with it or to replace the trigger assembly with a Double Set Double Lever trigger assembly.